1. Field of the Invention
The present invention relates to an organic light emitting display device. More specifically, the present invention relates to an organic light emitting display device in which permeation of exterior moisture can be prevented, dark defects caused by foreign materials can be improved and lifespan can thus be improved by changing the structure and manufacturing method of thin film encapsulation layer, and a method for manufacturing the same.
2. Discussion of the Related Art
Image display devices that realize a variety of information on the screen are core techniques of the information and telecommunication age, which are developed into thinner, lighter weight, portable and high-performance forms. In addition, bendable and flexible displays are required in pursuit of spatiality and convenience, and organic light emitting display devices to control an emitted light amount of an organic light emitting layer as display devices attract much attention recently.
Such an organic light emitting display device includes an organic light emitting element which includes an anode, an organic light emitting layer and a cathode laminated in this order on a substrate and a capping layer to cap the organic light emitting element.
The organic light emitting element is operated based on the following principle. That is, when an electric field is applied to a cathode and an anode disposed on both ends of the organic light emitting layer, electrons and holes injected and transported in the organic light emitting layer are recombined. The organic light emitting element uses electroluminiscence in which light is emitted by a bonding energy during this recombination. Electrons and holes are paired in the organic light emitting layer and then fall from an excited state to a bottom state to emit light.
In addition, the organic light emitting display device can be advantageously realized as a thin film. However, the organic light emitting display device has disadvantages in that deterioration due to internal factors such as deterioration of electrodes and light emitting layers due to oxygen and deterioration due to reaction between the light emitting layer and the interface, and deterioration due to exterior factors such as moisture, oxygen and UV light readily occur. Accordingly, it is considerably important to package and encapsulate the organic light emitting display device.
Hereinafter, the problems of an organic light emitting display device of the related art to which encapsulation is applied will be described.
FIG. 1 is a view illustrating the effect of foreign materials on an organic light emitting display device of the related art.
As shown in FIG. 1, an organic light emitting display device of the related art includes a substrate 10, an organic light emitting element array 20 disposed thereon and an encapsulation layer 30 including an inorganic film and an organic film laminated in this order, to protect the organic light emitting element array 20. Here, the encapsulation layer 30 has a substantially uniform thickness in a region in which the organic light emitting element array 20 is formed and display is substantially realized or at the edge of the region. Otherwise, the thickness of the encapsulation layer 30 may decrease at the edge due to properties of film formation.
Here, non-described reference numeral “21” means a bank to divide respective pixels of an organic light emitting element array and define respective light emitting layer formation regions.
When, during formation of the encapsulation layer 30, a foreign material 40 is present at the edge of the substrate 10, moisture permeation in which moisture is permeated along the foreign material 40, or an outgassing phenomenon in which gas generated in the foreign material 40 directly affects operation of the organic light emitting element array 20 may occur.
Meanwhile, in a case in which the encapsulation layer 30 is thickly formed, in order to reduce effects of the foreign material 40, disadvantageously, the thickness of the manufactured organic light emitting display device is increased, manufacturing costs increase and yield is deteriorated. In particular, the organic light emitting element array 20 also causes a secondary problem such as decrease in luminance due to large thickness. Accordingly, simple increase in thickness of the encapsulation layer 30 is limited. The method for manufacturing an organic light emitting display device of the related art cannot avoid effects of moisture permeation by foreign material or outgassing.
FIGS. 2A and 2B are images illustrating a foreign material produced at the edge of a deposition mask and moisture permeation of the side of the organic light emitting display device manufactured using the deposition mask.
FIG. 2A illustrates an edge of a deposition mask used for forming an encapsulation layer and, in particular, a state in which a foreign material is produced on the edge which contacts the substrate. FIG. 2B illustrates a state in which, when the deposition mask of FIG. 2A is used, moisture permeation of the side surface is caused by the foreign material and dark spots of elements adjacent to the edge of the organic light emitting display device are produced. As can be seen from these images, in the edge of the organic light emitting display devices, effects of the foreign material are serious.
The organic light emitting display device of the related art has the following problems.
In the process of forming the encapsulation layer, a great amount of foreign materials are produced in the edge of a deposition mask which directly contacts the substrate. For this reason, foreign materials are generally produced on the edge of the substrate.
Once a foreign material is present on the substrate, permeation of moisture in which moisture is permeated through the foreign material, or an outgassing phenomenon in which a gas generated in the foreign material directly affects operation of the organic light emitting element array may occur, unless the foreign material is completely covered via encapsulation.
However, an increase in thickness of the encapsulation layer in order to reduce effects of the foreign material entails restriction due to deterioration in yield and luminance. There is a difficulty in forming an encapsulation layer which has a sufficient thickness to block foreign materials.